羟基自由基氧化对蛋清蛋白质结构的影响

摘要

研究蛋清蛋白质经过FeCl3/抗坏血酸(Asc)/H2O2产生的羟基自由基氧化体系氧化后化学结构的变化.用不同浓度的H2O2(0、1、5、10和20 mmol/L)对蛋清蛋白质氧化3h,研究氧化前后蛋清蛋白质羰基、游离巯基、总巯基、游离氨基、粒径分布及二级结构的变化趋势.结果表明:氧化可使蛋清蛋白质羰基含量显著升高(p＜0.05),游离巯基和总巯基含量显著下降(p＜0.05),游离氨基显著下降(p＜0.05),平均粒径逐渐增大.当H2O2浓度为20 mmol/L时,与对照组相比羰基含量增加2.01倍,游离氨基降低了29.1％,平均粒径增加到666 nm.在H2O2浓度低于5 mmol/L时,α-螺旋和β-折叠含量升高,β-转角降低;H2O2浓度高于5 mmol/L时蛋清蛋白质的肽链发生断裂,进一步导致蛋白质结构发生了变化.以上结果表明氧化能在一定程度上改变蛋清蛋白的结构特性.%The objective of this study was to determine structural changes,including carbonyls,sulfhydryls,free amino,particle size distribution,secondary structure in egg white protein exposed to FeCl3/Asc/H2O2 hydroxyl radical-generating systems.Protein carbonyl content in EWP increased(p ＜ 0.05)with increasing concentrations of H2O2,free SH,total SH groups and free amino decreased (p ＜ 0.05)in a similar fashion.EWP average particle size increased.When the H2O2 concentration was increased to 20 mmol/L,there was 2.01-fold increase in carbonyl group,29.1％ decrease in free amino acid,compared with control group.The average particle size reached 666 nm.The results showed that there were increases in α-helix and β-fold of relative content,decrease in β-turn of relative content with the increase of oxidizing agent(H2O2 ＜ 5 mmol/L).Higher level oxidation (H2O2 ＞ 5 mmol/L)would induce fragmentation through direct breakage of peptide bonds,resulted in changes in the secondary structures.These oxidation-induced changed demonstrate high susceptibility of EWP to oxidative stress.